Electrical Stimulation of Broca's Area Enhances Implicit Learning of an Artificial Grammar (original) (raw)

Connectivity of the hippocampus and Broca's area during acquisition of a novel grammar

NeuroImage, 2018

A B S T R A C T Following Opitz and Friederici (2003) suggesting interactions of the hippocampal system and the prefrontal cortex as the neural mechanism underlying novel grammar learning, the present fMRI study investigated functional connectivity of bilateral BA 44/45 and the hippocampus during an artificial grammar learning (AGL) task. Our results, contrary to the previously reported interactions, demonstrated parallel (but separate) contributions of both regions, each with their own interactions, to the process of novel grammar acquisition. The functional connectivity pattern of Broca's area pointed to the importance of coherent activity of left frontal areas around the core language processing region for successful grammar learning. Furthermore, connectivity patterns of left and right hippocampi (predominantly with occipital areas) were found to be a strong predictor of high performance on the task. Finally, increasing functional connectivity over time of both left and right BA 44/45 with the right posterior cingulate cortex and the right temporo-parietal areas points to the importance of multimodal and attentional processes supporting novel grammar acquisition. Moreover, it highlights the right-hemispheric involvement in initial stages of L2 learning. These latter interactions were found to operate irrespective of the task performance, making them an obligatory mechanism accompanying novel grammar learning.

Neural Correlates for the Acquisition of Natural Language Syntax

Neuroimage, 2002

Some types of simple and logically possible syntactic rule never occur in human language grammars, leading to a distinction between grammatical and nongrammatical syntactic rules. Comparison of the neuroanatomical correlates underlying the acquisition of grammatical and nongrammatical rules can provide relevant evidence on the neural processes dedicated to language acquisition in a given developmental stage. Until present no direct evidence on the neural mechanisms subserving language acquisition at any developmental stage has been supplied. We used fMRI in investigating the acquisition of grammatical and nongrammatical rules in the specified sense in 14 healthy adults. Grammatical rules compared with nongrammatical rules specifically activated a left hemispheric network including Broca's area, as shown by direct comparisons between the two rule types. The selective role of Broca's area was further confirmed by time ؋ condition interactions and by proficiency effects, in that higher proficiency in grammatical rule usage, but not in usage of nongrammatical rules, led to higher levels of activation in this area. These findings provide evidence for the neural mechanisms underlying language acquisition in adults.

Artificial syntactic violations activate Broca's region

Cognitive Science, 2004

In the present study, using event-related functional magnetic resonance imaging, we investigated a group of participants on a grammaticality classification task after they had been exposed to well-formed consonant strings generated from an artificial regular grammar. We used an implicit acquisition paradigm in which the participants were exposed to positive examples. The objective of this study was to investigate whether brain regions related to language processing overlap with the brain regions activated by the grammaticality classification task used in the present study. Recent meta-analyses of functional neuroimaging studies indicate that syntactic processing is related to the left inferior frontal gyrus (Brodmann's areas 44 and 45) or Broca's region. In the present study, we observed that artificial grammaticality violations activated Broca's region in all participants. This observation lends some support to the suggestions that artificial grammar learning represents a model for investigating aspects of language learning in infants [TICS 4 (2000) 178] and adults [

Investigations of the syntax-brain relationship (Doctoral Dissertation)

This dissertation critically examines extant hypotheses on the syntax-brain relationship, particularly proposals concerning Broca’s area, and presents empirical data in efforts to localize syntactic operations in the brain. Chapter 2 of the dissertation reviews arguments for and against a role for Broca’s area in syntax, and presents an fMRI experiment using a construction called backward anaphora in which the activity in the pars triangularis of Broca’s area is shown to pattern with how sentences are processed (i.e., whether the construction involves active processing), and not their syntactic properties (i.e., activity is not contingent on Movement constructions). Chapter 3 extends Dehaene & Cohen’s neuronal recycling hypothesis (Dehaene & Cohen, 2007) to language function in Broca’s area to account for sentence-selective activations in this region of cortex (Fedorenko et al., 2012). In particular, the discussion in Chapter 3 focuses on language- or sentence-specific working memory (Caplan & Waters, 1999), and how language-specific working memory may develop out of domain-general working memory. Chapter 4 presents an fMRI experiment aimed at uncovering the neural basis of syntax using a “syntactic perturbation” technique during overt sentence production. In addition, the experiment specifically examined the response profile of Broca’s area and another region classically implicated in structural processing, the anterior temporal lobe (ATL), to our novel manipulation targeting syntactic structure. The results, when compared to perturbation in a control condition of unstructured word lists, revealed preferential activation for syntactic perturbation in networks previously implicated in motor control (Tourville et al., 2008) and action inhibition (Aron et al., 2014), including the basal ganglia, thalamus, and right inferior frontal gyrus, suggesting that (i) sentence production allows greater phonological/articulatory planning than list production, and (ii) syntax may rely on networks similar to basic motor control. However, effects at the syntax level are conflated with effects at lower motor levels in our experiment. Broca’s area and the ATL did not exhibit effects consistent with syntactic processing, although our results extended the basic finding of increased activation to sentences compared to word lists previously found in the ATL (Mazoyer et al., 1993). Finally, Chapter 5 concludes the dissertation.

What artificial grammar learning reveals about the neurobiology of syntax

Brain and Language, 2012

In this paper we examine the neurobiological correlates of syntax, the processing of structured sequences, by comparing FMRI results on artificial and natural language syntax. We discuss these and similar findings in the context of formal language and computability theory. We used a simple right-linear unification grammar in an implicit artificial grammar learning paradigm in 32 healthy Dutch university students (natural language FMRI data were already acquired for these participants). We predicted that artificial syntax processing would engage the left inferior frontal region (BA 44/45) and that this activation would overlap with syntax-related variability observed in the natural language experiment. The main findings of this study show that the left inferior frontal region centered on BA 44/45 is active during artificial syntax processing of well-formed (grammatical) sequence independent of local subsequence familiarity. The same region is engaged to a greater extent when a syntactic violation is present and structural unification becomes difficult or impossible. The effects related to artificial syntax in the left inferior frontal region (BA 44/45) were essentially identical when we masked these with activity related to natural syntax in the same subjects. Finally, the medial temporal lobe was deactivated during this operation, consistent with the view that implicit processing does not rely on declarative memory mechanisms that engage the medial temporal lobe. In the context of recent FMRI findings, we raise the question whether Broca's region (or subregions) is specifically related to syntactic movement operations or the processing of hierarchically nested non-adjacent dependencies in the discussion section. We conclude that this is not the case. Instead, we argue that the left inferior frontal region is a generic on-line sequence processor that unifies information from various sources in an incremental and recursive manner, independent of whether there are any processing requirements related to syntactic movement or hierarchically nested structures. In addition, we argue that the Chomsky hierarchy is not directly relevant for neurobiological systems.

Grammatical Distinctions in the Left Frontal Cortex

Journal of Cognitive Neuroscience, 2001

& Selective deficits in producing verbs relative to nouns in speech are well documented in neuropsychology and have been associated with left hemisphere frontal cortical lesions resulting from stroke and other neurological disorders. The basis for these impairments is unresolved: Do they arise because of differences in the way grammatical categories of words are organized in the brain, or because of differences in the neural representation of actions and objects? We used repetitive transcranial magnetic stimulation (rTMS) to suppress the excitability of a portion of left prefrontal cortex and to assess its role in producing nouns and verbs. In one experiment subjects generated real words; in a second, they produced pseudowords as nouns or verbs. In both experiments, response latencies increased for verbs but were unaffected for nouns following rTMS. These results demonstrate that grammatical categories have a neuroanatomical basis and that the left prefrontal cortex is selectively engaged in processing verbs as grammatical objects. &

Neural correlates of syntactic transformations

Human brain …, 2004

Many agrammatic aphasics have a specific syntactic comprehension deficit involving processing syntactic transformations. It has been proposed that this deficit is due to a dysfunction of Broca's area, an area that is thought to be critical for comprehension of complex transformed sentences. The goal of this study was to investigate the role of Broca's area in processing canonical and non-canonical sentences in healthy subjects. The sentences were presented auditorily and were controlled for task difficulty. Subjects were asked to judge the grammaticality of the sentences while their brain activity was monitored using event-related functional magnetic resonance imaging. Processing both kinds of sentences resulted in activation of language-related brain regions. Comparison of non-canonical and canonical sentences showed greater activation in bilateral temporal regions; a greater activation of Broca's area in processing antecedent-gap relations was not found. Moreover, the posterior part of Broca's area was conjointly activated by both sentence conditions. Broca's area is thus involved in general syntactic processing as required by grammaticality judgments and does not seem to have a specific role in processing syntactic transformations. Hum. Brain Mapp. 22:72 -81, 2004.

How left inferior frontal cortex participates in syntactic processing: Evidence from aphasia

Brain and Language, 2008

We report on three experiments that provide a real-time processing perspective on the poor comprehension of Broca's aphasic patients for non-canonically structured sentences. In the first experiment we presented sentences (via a Cross Modal Lexical Priming (CMLP) paradigm) to Broca's patients at a normal rate of speech. Unlike the pattern found with unimpaired control participants, we observed a general slowing of lexical activation and a concomitant delay in the formation of syntactic dependencies involving ''moved'' constituents and empty elements. Our second experiment presented these same sentences at a slower rate of speech. In this circumstance, Broca's patients formed syntactic dependencies as soon as they were structurally licensed (again, a different pattern from that demonstrated by the unimpaired control group). The third experiment used a sentence-picture matching paradigm to chart Broca's comprehension for non-canonically structured sentences (presented at both normal and slow rates). Here we observed significantly better scores in the slow rate condition. We discuss these findings in terms of the functional commitment of the left anterior cortical region implicated in Broca's aphasia and conclude that this region is crucially involved in the formation of syntactically-governed dependency relations, not because it supports knowledge of syntactic dependencies, but rather because it supports the real-time implementation of these specific representations by sustaining, at the least, a lexical activation rise-time parameter. Published by Elsevier Inc.